Team:
I'm going to weigh in later tonight after several notes in this thread,
but want to respond to this ASAP.
I very strongly feel that we should try our best to get the CAN-Do!
widget to work with receivers. I don't care if it's redesign,
shielding, both, or whatever.
Rationale:
In my demented mind, there are three mandatory requirements for EMI -- a
source, a path (conducted or emitted), and a victim receptor.
We will need to work on all three, but (to a point) working on the
source has the most bang for the buck. I say this because, we might do
a nice job of shielding a particular receiver, but if we ignore the
source, we run a huge risk of unintended and unexpected/untested
collateral effects -- like there being so much radiated noise that the
noise floor at some antenna is unacceptable. Reducing source
strength.reduces total radiated noise by a factor of however many
widgets we fly.
That said, I'm ABSOLUTELY willing to be convinced that, "We've done
this, we've spent that, any more is diminishing returne."
I truly feel that we should do our best to limit the source as part of
an integrated attack on this issue.
More later tonight.
Thanks & 73,
Jim
wb4gcs at amsat.org
Chuck Green wrote:
>Hi Juan,
>>I agree that specifications prior to design would be helpful
>(required?). But as far as the EMI issues are concerned, we do seem to
>have a chicken/egg problem. And I'm not sure it is practical to design
>a widget that meets the requirements of receiver modules. Most modules
>simply don't need anything nearly this good. But we should do
>everything practical to accommodate receiver modules, and maybe meet
>their requirements completely.
>>Thanks,
>Chuck
>>Juan Rivera wrote:
>>>>Chuck,
>>>>My comments might have been buried in the flurry of email a while back.
>>Things seem a bit quieter now so here they are:
>>>>1) Don't get too far into a redesign until a top-level EMI requirement is
>>created. This can't be done properly until prototype solar panel power
>>converters are fabricated and tested. I would work to create a new power
>>supply with a switching frequency of at least 500 kHz while you wait
>>however. This will make filtering much easier, the filter components will
>>be smaller, and any spurs that make it into the receiver will be outside the
>>passband of the IF.
>>>>2) The EMI requirements for radiated and conducted emissions and
>>susceptibility should flow out of that test data and not be guesses.
>>>>3) Once we have an EMI requirement then tradeoffs need to be considered
>>between the CAN-Do module and the enclosure - one or two compartment? Sheet
>>metal or milled construction? The results of that tradeoff study will
>>determine how much room you have to work with, how much front panel space,
>>and how much shielding and filtering are required.
>>>>If I had my way the enclosure would be a two-cell milled enclosure with all
>>the RF and IF exiting out the side of the rear cell. The CAN-Do module and
>>the Receiver switching power supply would both be located in the first cell
>>with feed-thru filtering in the common bulkhead between cells (all digital
>>power in the front and all analog in the rear). That would mean that the
>>CAN-Do connector would be the only connector on the front of the case. If
>>that were true then the only reason to change connectors would be to save
>>weight or increase reliability. It would also mean that the existing CAN-Do
>>PCB footprint would be fine as it is.
>>>>In my presentation I will suggest that the next revision of the 70 cm
>>receiver should be postponed until all of these issues are resolved.
>>>>73,
>>>>Juan
>>>>>>>>-----Original Message-----
>>From: eagle-bounces at amsat.org [mailto:eagle-bounces at amsat.org] On Behalf Of
>>Chuck Green
>>Sent: Monday, July 16, 2007 7:47 PM
>>To: Louis McFadin
>>Cc: Dave Black ((Work)); Dave Black ((Home)); David Smith; AMSAT Eagle;
>>Samsonoff at Mac. Com; Juan.Rivera ((Work))
>>Subject: [eagle] Re: CAN-Do-Too! ??????????
>>>>Thanks, Lou.
>>>>I don't know of any reason not to use them either. Obviously, it needs
>>to meet our mounting configuration requirement so the new mechanical
>>design can meet the objectives I stated earlier. This means it must
>>mount on the edge of a PCB. I think the HD15-D has three rows of pins
>>so I'm not sure how this can work, but I haven't looked at the various
>>parts available so maybe this problem has been solved.
>>>>If we are going to seriously consider using HD connectors I think we
>>need the blessing of AMSAT's VP of Engineering and the EAGLE project
>>coordinator. This would be true for any change that would be pervasive
>>in the satellite.
>>>>I am a little disappointed that there have not been any comments
>>regarding the changes I saw as being made with a new design.
>>Additions/changes/questions/etc. I don't think we should do a new
>>design without this discussion. Maybe people feel these issues have
>>been well covered in the past. If so, a simple "looks good to me" would
>>be helpful.
>>>>And no one has stepped up to say they are well qualified and will design
>>a new power supply. Without this, I don't see a new design happening,
>>but maybe.
>>>>And finally, I see that no one has dared touch the subject of parts
>>procurement I raised.
>>>>Obviously, most of these comments are really meant for the Cc list.
>>>>Thanks,
>>Chuck
>>>>Louis McFadin wrote:
>>>>>>>>>Chuck,
>>>Mouser has a very large selection of D-sub connectors including the
>>>high density versions. Most are in stock.
>>>I see no inherent reason for not using them.
>>>>>>Lou McFadin
>>>W5DID
>>>w5did at mac.com <mailto:w5did at mac.com>
>>>>>>>>>On Jul 16, 2007, at 7:19 PM, Chuck Green wrote:
>>>>>>>>>>>>>>>>I have had one experience with the high density D connectors. They
>>>>were much larger pin count than 9 or 15! After someone absolutely
>>>>insisted that we use them I did the board lay out. Turned out that
>>>>they were *totally* unavailable!!! I did the board layout
>>>>again@#$%&^* using standard Sub-D's. That was a number of years ago
>>>>so I would hope things have changed. If someone is absolutely
>>>>confident they can obtain the parts we need then I'm not at all
>>>>opposed to using them (remember, I'm not volunteering to do parts
>>>>procurement for this project; this is a good time to use someone
>>>>that's good at parts procurement).
>>>>>>>>While at Goddard for P3D vib test I noticed NASA satellites using
>>>>standard Sub-D's. That was also a few years ago. Anyone know of
>>>>High Density Sub-D's being used on other satellites?
>>>>>>>>Chuck
>>>>>>>>Bdale Garbee wrote:
>>>>>>>>>>>>>>>>>On Tue, 2007-07-10 at 09:02 -0700, Chuck Green wrote:
>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>The sub-miniature D connector series has served us well. If anyone
>>>>>>has *experience* with something they think might be a better
>>>>>>choice, we'd love to hear about it.
>>>>>>>>>>>>>>>>>>>>>>>>>>>>>At the AMSAT annual meeting that was held near Washington, D.C., a
>>>>>couple of years ago (three?), someone approached me after the CAN-Do!
>>>>>talk that Stephen and I gave to ask why we weren't using the
>>>>>higher-density connectors that put 15 pins in the same shell size as the
>>>>>9-pin version of the series we have been using... and followed up by
>>>>>sending me what looked like mil/aero-spec samples of such a part that I
>>>>>probably still have in my basement somewhere. I'm sorry that I can't
>>>>>recall at all who that person was, but it was someone who claimed to be
>>>>>using such connectors professionally with good results.
>>>>>>>>>>At the time, we weren't likely to be redesigning the units any time
>>>>>soon, so I didn't take any action on this suggestion. If we're going to
>>>>>revisit the design and think we need more than 9 pins, it might be worth
>>>>>investigating higher density connectors like that?
>>>>>>>>>>Bdale
>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>_______________________________________________
>>Via the Eagle mailing list courtesy of AMSAT-NA
>>Eagle at amsat.org>>http://amsat.org/mailman/listinfo/eagle>>>>>>>>>>>>>_______________________________________________
>Via the Eagle mailing list courtesy of AMSAT-NA
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